Herbicidal compositions

ABSTRACT

A method of avoiding the toxifying effect of a salt of a herbicidal bipyridylium quaternary cation ingested by a human which comprises administering to said human an emetically effective amount of an s-triazolo[1,5-a]pyrimidine derivative.

This is a continuation of application Ser. No. 716,801, filed Aug. 23,1976, now U.S. Pat. No. 4,046,552.

This invention relates to herbicidal compositions containing aherbicidal bipyridylium quaternary salt as an active ingredient.

Over the years, a wide range of pesticides has been developed foragricultural use in the control of fungal and insect pests and weeds.While these substances are necessarily toxic to certain forms of life,when used with due care and in accordance with governmentally approvedcodes of practice, they present no hazard to human life. However, inspite of efforts to encourage those concerned with pesticides to adoptsafe handling practices, instances of misuse of pesticides do occur. Oneparticular unsafe practice in the case of liquid pesticides is for anoperator to transfer a small amount of the concentrated pesticide to adomestic container such as a beverage bottle for subsequent use at home.The risk attached to these practices is of course that a child orincautious adult coming upon the bottle may swallow the contents withpossibly serious consequences.

We have now found it possible to reduce the likelihood of seriousconsequences of such accidental swallowing by induction of emesis. Thiscan result in some cases in the rapid removal of the pesticidalcomposition from the stomach and digestive tract before lethal amountsof the pesticide can be assimilated by the body.

We have further discovered that the admixture of a knowntriazolo[1,5-a]pyrimidine derivative of formula (I), as specifiedhereinafter, to a herbicidal bipyridylium quaternary salt in aherbicidal composition produces a composition which if swallowed tendsto induce emesis, and thereby, expulsion of the composition.

According to the invention there is provided a herbicidal composition ofreduced health hazard comprising a salt of a herbicidal bipyridyliumquaternary cation and an effectively emetic amount of as-triazolo-[1,5-a]-pyrimidine derivative of the formula: ##STR1##wherein R¹ is hydrogen, a C₁₋₄ alkyl radical, or a COOEt radical, R² isa C₁₋₄ alkyl radical or an allyl radical, and R³ is a C₁₋₄ alkylradical; and addition salts thereof. The s-triazolo[1,5-a]pyrimidinering structure is numbered as shown below: ##STR2##

Particular derivatives of 5-oxo-4,5-dihydro-s-triazolo[1,5-a]pyrimidineof use in the practice of the invention are:

6-methyl-4-n-propyl-2-n-propylamino-

2-amino-6-methyl-4-allyl-

2-amino-4,6-di-n-propyl-

2-ethoxycarbonylamino-6-methyl-4-n-propyl-

An especially useful triazolo-pyrimidine for use in the compositions ofthe invention is2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(II). ##STR3##

Preferred herbicidal bipyridylium quaternary salts for use in thecompositions of the invention are those of the following formulae:##STR4## wherein R and R¹, which may be the same or different, stand foralkyl radicals of from 1 to 4 carbon atoms which may be substituted byhydroxyl, halogen, carboxyl, alkoxy, alkylcarbonyl, alkoxycarbonyl,carbamoyl or N-substituted carbamoyl; [X]^(n-) represents an anion and nis an integer from 1 to 4 inclusive.

Particularly preferred herbicidal bipyridylium quaternary salts arethose listed below:

1,1-dimethyl-4,4'-bipyridylium di(methylsulphate) (paraquatdimethosulphate)

1,1'-ethylene-2,2'-bipyridylium dibromide (diquat dibromide)

1,1'-dimethyl-4,4'-bipyridylium dichloride (paraquat dichloride)

1,1'-di-2-hydroxyethyl-4,4'-bipyridylium dichloride

1-(2-hydroxyethyl-1'-methyl-4,4'-bipyridylium dichloride

1,1'-di-carbamoylmethyl-4,4'-bipyridylium dichloride

1,1'-bis-N,N-dimethylcarbamoylmethyl-4,4'-bipyridylium dichloride

1,1'-dimethyl-4,4'-bipyridylium sulphate (paraquat sulphate)

1,1'-bis-N,N-diethylcarbamoylmethyl-4,4'-bipyridylium dichloride

1,1'-diacetonyl-4,4'-bipyridylium dichloride

1,1'-diethoxycarbonylmethyl-4,4'-bipyridylium dibromide

1,1'-diallyl-4,4'-bipyridylium dibromide

The names in brackets alongside some of the compounds in the above listare the accepted common names for the cationic portion of thesecompounds. Thus `paraquat` is the common name for the1,1'-dimethyl-4,4'-bipyridylium cation. Paraquat is a particularlypreferred bipyridylium compound for use in the compositions of theinvention. A particularly preferred anion [X]^(n-) is the chlorideanion, for reasons of convenience and economy, but any anion which givesrise to a conveniently water-soluble salt may be used if desired. Theherbicidal action is due solely to the cation and for this reason theconcentration of a herbicidal bipyridylium salt compositions isfrequently given in terms of the cation alone. The amount of herbicidalbipyridylium quaternary salt present in the compositions of theinvention is generally from 1.0 to 99.9% by weight.

The compositions of the invention may be solids, e.g. granules, orliquids, e.g. aqueous solutions.

In a preferred aspect the invention provides a concentrated herbicidalcomposition comprising an aqueous solution of a salt of a herbicidalbipyridylium quaternary cation and an effectively emetic amount of atriazolo-pyrimidine as hereinbefore defined. Preferably the herbicidalbipyridylium quaternary cation is paraquat.

The amount of herbicidal bipyridylium quaternary cation present in theaqueous solution is preferably from 0.05 to 4.0 pounds per Imperialgallon (50 grams to 400 grams per liter).

Preferably the composition also comprises a surface active agent.

Surface-active agents may be cationic, non-ionic or anionic. Generallyspeaking cationic and non-ionic surface-active agents are preferred toanionic surface-active agents for use in the compositions of theinvention, since the latter may interact undesirably with thebipyridylium quaternary salt in the compositions. Examples of non-ionicsurface-active agents for use in the compositions of the inventioninclude the condensation products of ethylene oxide with alkyl phenolssuch as octylphenol, nonylphenol and octylcresol. Other non-ionic agentsare the partial esters derived from long chain fatty acids and hexitolanhydrides, for example sorbitan monolaurate; the condensation productsof the said partial esters with ethylene oxide; and the lecithins.Examples of cationic surface-active agents include quaternary salts andcondensates of ethylene oxide with amines, for example the substancessold under the Trade Mark "Ethomeen", "Ethoduomeen", "Duoquad" and"Arquad".

Particularly preferred surface-active agents are the combinations ofsurface-active agents described in U.K. Pat. No. 998,264 for use informulations of herbicidal bipyridylium quaternary salts.

The preparation of the triazolo-pyrimidines (I) has been described inU.S. Pat. Nos. 3,689,488 and 3,773,949; which description is hereinincorporated by reference.

The emetic properties of the composition are primarily determined by theamount of triazolo-pyrimidine it contains. In deciding the mostappropriate amounts of triazolo-pyrimidine to use in any composition,regard must be had to the efficacy of the triazolo-pyrimidine relativeto the toxicity of the herbicide. The amount of triazolo-pyrimidine tobe included is preferably such that a sample of the compositioncontaining a potentially lethal dose of herbicide contain sufficient ofthe triazolo-pyrimidine to give it an emetic action. However, clearlyneither lethal doses nor emetic doses can be directly measured in man;they can only be inferred from animal data.

Compositions according to the invention preferably contain from 0.1 to 5parts by weight of the triazolo-pyrimidine (I) per 100 parts of theherbicidal bipyridylium quaternary cation. Conveniently the amount ofthe triazolo-pyrimidine (I) used is 0.25 to 2.0 parts per 100 parts ofherbicidal bipyridylium quaternary cation.

Concentrated aqueous formulations of the invention are corrosive. Theymust be handled with care, to avoid splashing on the eyes or skin, andthey should not be allowed to come into contact with corrodeable metalsprior to dilution.

The compositions according to the invention may also comprise coloureddyestuff or pigment compounds. Examples of such compounds are "MonastralBlue BNV Paste" and "Lissamine Turquoise VN 150".

The compositions according to the invention may also comprise astenching agent. Examples of such stenching agents are alkyl pyridinesas described in U.S. Pat. No. 3,920,443; which description isincorporated herein by reference.

If desired, the triazolo-pyrimidines (I) may be incorporated inthixotropic formulations of herbicidal quaternary salts. In particularthe triazolo-pyrimidines (I) may be incorporated in the formulations ofherbicidal bipyridylium quaternary salts described in our U.K. patentSpecification No. 1,395,502; which description is incorporated herein byreference. These formulations comprise an aqueous solution of aherbicidal bipyridylium quaternary salt containing a gelling agent, forexample finely divided silica, or a combination of the xanthan gum soldunder the trade name "Kelzan" with sodium metaborate. Xanthan gum is acomplex polysaccharide.

The composition according to the invention may also comprise a herbicideother than a herbicidal bipyridylium quaternary salt as hereinbeforedefined. Examples of such herbicides are:

Amides (e.g. N,N-diallylchloroacetamide, 3,4-dichloropropionanilide,N-(3-chloro-4-methyl-phenyl)-2-methylpentamide).

Carbamates (e.g. Isopropyl-N-phenylcarbamate,isopropyl-N-(3-chlorophenyl)carbamate, 4-chloro-2but-2-ynyl-N-(3-chlorophenyl)carbamate,2-chlorallyl-N,N-diethyl-dithiocarbamate).

Ureas/anilides (e.g. N,N'-di-(2,2,2-trichloro-1-hydroxyethyl)urea,3,4-dichloroacetanilide, O-chloroisobutyranilide,α-bromo-3,4-dichloroacetanilide, 3,4-dichloroformanilide,2-acetamido-3-chlorotoluene).

Diazines (e.g.3,4,5,6-tetrahydro-3,5-dimethyl-2-thio-2H-1,3,5-thiadiazine,5-bromo-3-isopropyl-6-methyluracil,5-amino-4-chloro-2-phenyl-3-pyridazone,1,2,3,6-tetrahydro-3,6-dioxopyridazine).

Triazines (e.g. 2-chloro-4,6-bisethylamino-1,3,5-triazine,2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine,2-chloro-4,6-bisisopropylamino-1,3,5-triazine,4-ethylamino-6-isopropylamino-2-methoxy-1,3,5-triazine,4,6-bisisopropylamino-2-methoxy-1,3,5-triazine).

The inclusion of the triazolo-pyrimidine (I) in compositions accordingto the invention has, in most cases, no significant adverse effect uponthe herbicidal activity of the compositions. The invention isillustrated by the following Examples.

EXAMPLE 1

This Example illustrates a composition according to the invention whichcomprises2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(II) in aqueous solution.

    ______________________________________                                        Ingredients          % w/v                                                    ______________________________________                                        Paraquat concentrate x                                                        (II)                 0.05                                                     Water                to 100 ml                                                (where x gives 200 ± 5 g/liter paraquat cation)                            ______________________________________                                    

Paraquat concentrate is a solution of paraquat dichloride containing 25%to 30% by weight of 1,1'-dimethyl-4,4'-bipyridylium cation. The amountspecified in the table above was sufficient to give a compositioncontaining 20% by weight of paraquat cation. The composition wasprepared by simple agitation of the ingredients together.

EXAMPLE 2

This Example illustrates a composition according to the invention whichcomprises the triazolo-pyrimidine (II) in aqueous solution. Thecomposition comprises the following ingredients.

    ______________________________________                                        Ingredients          % w/v                                                    ______________________________________                                        Paraquat concentrate x                                                        Sodium metaborate    1.3                                                      Sodium benzoate      2.0                                                      Lissapol NX          1.1                                                      DS 4392              4.1                                                      Silcolapse 5000       0.06                                                    (II)                  0.05                                                    Water                to 100 ml                                                (where x gives 200 ± 5 g/liter paraquat cation)                            ______________________________________                                    

"Lissapol" NX is a Trade Mark for a surface-active agent comprising acondensate of from 7 to 8 molar proportions of ethylene oxide with 1molar proportion of p-nonylphenol.

DS 4392 is a code number for a surface-active agent comprising a mixtureof amines derived from soya bean fatty acids condensed withapproximately 15 molar proportions of ethylene oxide.

"Silcolapse" is a Trade Mark for an anti-foaming agent comprising asilicone derivative.

The composition described above was prepared by simple agitation of theingredients together.

EXAMPLE 3

This Example illustrates a composition according to the invention whichcomprises a gelling agent in addition to the triazolo-pyrimidine (II).The composition comprises the following ingredients.

    ______________________________________                                        Ingredients       Amount in Grams                                             ______________________________________                                        Paraquat concentrate                                                                            x                                                           "Kelzan"          0.4 (added as 1%                                                              solution in water)                                          Sodium metaborate  0.014                                                      Lissapol NX       1.1                                                         DS 4392           4.1                                                         (II)               0.05                                                       Silcolapse 5000    0.01                                                       Water             to 100 ml                                                   (where x gives 200 ± g/liter paraquat ion)                                 ______________________________________                                    

The composition described above was prepared by simple agitation of theingredients together and was sufficiently fluid when prepared to bepoured into containers. On standing for 15 to 20 minutes the compositionformed a gel and was not pourable unless vigorously shaken.

EXAMPLE 4

This Example illustrates a dry free flowing granular composition whichis both stable in storage and is readily convertible into an aqueoussolution for application as a spray.

A solution was made up having the following composition in whichpercentages are by weight.

    ______________________________________                                        Paraquat dichloride      33.0                                                 2-amino-6-methyl-5-oxo-4-n-propyl-                                            4,5-dihydro-s-triazolo[1,5-a]                                                 pyrimidine (II)          0.1                                                  Sodium metaborate        2.5                                                  Potassium phosphate      1.6                                                  Lissapol NX              24.0                                                 Water                    38.8                                                                          100                                                  ______________________________________                                    

310 gms of the above solution were then added in a thin stream to 690gms of dried magnesium sulphate contained in the bowl of a HOBART C.E.100 dough mixer ("HOBART" is a Registered Trade Mark). The resultingproduct which was dry was then passed through a granulating machine andfinally agitated in a sieve having 30 meshes per linear inch to removedust. The resulting granules had a size of at least 0.9 mm and possesseda solution rate of 150 seconds.

EXAMPLE 5

This Example illustrates a composition according to the invention whichcomprises2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(II) and a stenching agent in aqueous solution.

    ______________________________________                                        Ingredients          % w/v                                                    ______________________________________                                        Paraquat concentrate x                                                        n-valeric acid       1.0                                                      II                    0.05                                                    DS 4392              4.0                                                      Silcolapse            0.01                                                    Lissapol NX          1.0                                                      Water                to 100 mls                                               (where x gives 200 g/l paraquat ion).                                         ______________________________________                                    

The compositions described above was prepared by simple agitation of theingredients together.

EXAMPLE 6

This Example illustrates a composition according to the invention whichcomprises2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(II) in a thickened, coloured, aqueous solution.

    ______________________________________                                        Ingredients          % w/v                                                    ______________________________________                                        Paraquat concentrate x                                                        Synperonic 2         2.5                                                      Synperonic 16        2.5                                                      Nansa 1106           8.5                                                      Monastral BNVS Paste 1.0                                                      Pyridine Base        1.0                                                      II                    0.05                                                    Water                to 100 mls                                               (where x gives 200 g/l paraquat ion).                                         ______________________________________                                    

"Synperonic" and "Nansa" are Trade Marks. Synperonic 2 is a condensationproduct of a mixture of 67% C₁₃ and 33% C₁₅ aliphatic alcohols with twoequivalents of ethylene oxide. Synperonic 16 is a condensation productof a mixture of 67% C₁₃ and 33% C₁₅ aliphatic alcohols with sixteenequivalents of ethylene oxide. Nansa 1106 is sodium dodecyl(substantially C₁₂ straight chain) benzene sulphonate. Monastral BNVSpaste is a dispersion comprising 15% w/v copper phthalocyanine pigmentin water. Pyridine base is a mixture comprising substantially basicalkyl pyridines.

EXAMPLE 7

This Example illustrates a composition according to the invention whichcomprises2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(II) in aqueous solution.

    ______________________________________                                        Ingredients             % w/v                                                 ______________________________________                                        diquat dibromide        x                                                     sodium molybdate        0.18                                                  potassium phosphate (as a mixture                                             of dipotassium hydrogen                                                       phosphate and potassium                                                       dihydrogen phosphate)   2.75                                                  (II)                    0.05                                                  water                   to 100 ml                                             (where x gives 140 ± 5 g/l diquat ion).                                    ______________________________________                                    

Diquat ion is 1,1'-ethylene-2,2'-bipyridylium cation. The compositiondescribed above was prepared by simple agitation of the ingredientstogether, and had a pH of 6.5±0.3.

EXAMPLE 8

This Example illustrates a composition according to the invention whichcomprises2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(II) in aqueous solution.

    ______________________________________                                        Ingredients          % w/v                                                    ______________________________________                                        Morfamquat dichloride                                                                              x                                                        II                   0.05                                                     water                to 100 mls                                               (where x gives 300 ± 5 g/l morfamquat ion).                                ______________________________________                                    

Morfamquat ion is1,1'-bis(3,5-dimethylmorpholinocarbonylmethyl)-4,4'-bipyridylium ion.The composition described above was prepared by simple agitation of theingredients together.

EXAMPLE 9

This Example illustrates a composition according to the invention whichcomprises2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(II) in aqueous solution.

    ______________________________________                                        Ingredients            % w/v                                                  ______________________________________                                        1,1'-bis(diethylcarbamoylmethyl)-                                             4,4'-bipyridylium dichloride                                                                         x                                                      Tween 20               8                                                      (II)                   0.05                                                   water                  to 100 mls                                             ______________________________________                                    

(where x gives 200±5 g/l1,1'-bis(diethylcarbamoylmethyl)-4,4'-bipyridylium ion). The compositiondescribed above was prepared by simple agitation of the ingredientstogether.

"Tween" is a Trade Mark. Tween 20 is a condensation product of one moleof sorbitan monolaurate with twenty moles of ethylene oxide.

EXAMPLE 10

This Example illustrates a composition according to the invention whichcomprises2-n-propylamino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidinein aqueous solution.

    ______________________________________                                        Ingredients             % w/v                                                 ______________________________________                                        Paraquat concentrate    x                                                     2-n-propylamino-6-methyl-5-oxo-4-n-                                           propyl-4,5-dihydro-s-triazolo                                                 [1,5-a] pyrimidine      0.05                                                  Water                   to 100 ml                                             ______________________________________                                        (where x gives 200 ± 5 g/liter paraquat cation                             ______________________________________                                    

EXAMPLE 11

This Example illustrates a composition according to the invention whichcomprises2-amino-5-oxo-4,6-di-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine inaqueous solution.

    ______________________________________                                        Ingredients             % w/v                                                 ______________________________________                                        Paraquat concentrate    x                                                     2-amino-5-oxo-4,6-di-n-propyl-4,5-                                            dihydro-s-triazolo [1,5-a]-                                                   pyrimidine              0.05                                                  Water                   to 100 ml                                             (where x gives 200 ± 5 g/liter paraquat cation)                            ______________________________________                                    

EXAMPLE 12

This Example illustrates a composition according to the invention whichcomprises2-ethoxycarbonylamino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidinein aqueous solution.

    ______________________________________                                        Ingredients             % w/v                                                 ______________________________________                                        Paraquat concentrate    x                                                     2-ethoxycarbonylamino-6-methyl-5-                                             oxo-4-n-propyl-4,5-dihydro-                                                   s-triazolo [1,5-a] pyrimidine                                                                         0.05                                                  Water                   to 100 ml                                             (where x gives 200 ± 5 g/liter paraquat cation)                            ______________________________________                                    

EXAMPLE 13

This Example illustrates a composition according to the invention whichcomprises2-amino-6-methyl-5-oxo-4-allyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidinein aqueous solution.

    ______________________________________                                        Ingredients             % w/v                                                 ______________________________________                                        Paraquat concentrate    x                                                     2-amino-6-methyl-5-oxo-4-allyl-4,5-                                           dihydro-s-triazolo [1,5-a]-                                                   pyrimidine              0.05                                                  Water                   to 100 ml                                             (where x gives 200 ± 5 g/liter paraquat cation)                            ______________________________________                                    

EXAMPLE 14

This Example illustrates the reduced likelihood of serious consequencesresulting from the ingestion of a herbicidal composition according tothe invention.

With monkeys. Male cynomolgus monkeys (Macaca fasicularis), body weightsin the range 3.5-5 kg, were used.

Test 1

Eight monkeys were dosed with a herbicidal bipyridylium quaternary saltcomposition as specified below containing 100 mg paraquat ion/kg bodyweight.

The required amount of a composition comprising:

    ______________________________________                                        Ingredients          % w/v                                                    ______________________________________                                        paraquat concentrate x                                                        Lissapol NX          1.1                                                      DS 4392              4.1                                                      Silcolapse 5000      0.01                                                     Water                to 100 ml                                                (where x gives 200 ± 5 g/l paraquat ion.)                                  ______________________________________                                    

was diluted with water to 20 ml to give 100 mg paraquat ion/kg bodyweight, and to which was added 10 g of `COMPLAN`. `COMPLAN` is a TradeMark for a carboxymethyl cellulose.

All eight of the monkeys died.

Test 2

Eight monkeys were dosed with a composition according to the inventioncomprising the same amount of the same composition (giving 100 mgparaquat ion/kg body weight) as specified in Test 1 plus2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(2 mg/kg body weight).

Only two of the monkeys died. The six animals that survived all vomitedin the first hour after dosing.

Test 3

Test 1 was repeated with four monkeys. All the monkeys died within 3-4days.

Test 4

Test 2 was repeated with four monkeys and carried out at the same timeas test 3.

All the monkeys vomited; two about 20 minutes after dosing, one afterapproximately 45 minutes, and one after approximately 8 hours. The threemonkeys which vomited early survived. The monkey which vomited laterdied.

With dogs. Male beagle dogs, body weight in the range 9-12 kg were used.

Test 5

Four dogs were dosed with a herbicidal bipyridylium quaternary saltcomposition as specified below at a rate of 20 mg paraquat ion/kg bodyweight.

    ______________________________________                                        Ingredients          % w/v                                                    ______________________________________                                        Paraquat concentrate x                                                        Water                to 50 ml                                                 ______________________________________                                    

To this solution was added 6 g `COMPLAN`.

(x to give 20 mg paraquat ion/kg body weight).

Three out of four of the dogs died within the first week of dosing.

Test 6

Four dogs were dosed with a composition according to the inventioncomprising the same amount of the same composition (giving 20 mgparaquat ion/kg body weight) as specified in Test 5 plus2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine(3 mg/kg body weight). All of the dogs vomited within an hour of beingdosed and none of them died.

Test 7

Test 5 was repeated but with the composition comprising 30 mg paraquation/kg body weight. Three out of the four dogs died.

Test 8

Test 6 was repeated but with the composition comprising 30 mg paraquation/kg body weight. All of the dogs vomited within an hour of beingdosed and none of them died.

Test 9

Test 6 was repeated but with the composition comprising 2 mg of2-amino-6-methyl-5-oxo-4-n-propyl-4,5-dihydro-s-triazolo[1,5-a]pyrimidine/kgbody weight. All four dogs vomited within 15 minutes and survived.

EXAMPLE 14

This Example illustrates the emetic potency of several members of thes-triazolo-[1,5-a]-pyrimidine class of the formula (I).

The pyrimidine derivatives were administered orally to Beagle dogs (bodyweight approximately 10 kg) either by gastric intubation (with thematerial in 50 ml of a 12.5% (w/v) `COMPLAN` suspension) or, when thematerial was particularly insoluble in water, by means of a gelatinecapsule. The Table shows the time within which emesis occurred.

    __________________________________________________________________________    Derivative of 5-oxo-4,5-dihydro-s-triazolo-                                                        Dose Time within which                                   [1,5-a] pyrimidine   mg/Dog                                                                             emesis occurred (min)                               __________________________________________________________________________    6-methyl-4-n-propyl-2-n-propylamino-                                                               25   30-60                                               2-amino-4,6-di-n-propyl-                                                                           25   30-60                                               2-ethoxycarbonylamino-6-methyl-4-n-propyl-                                                         25   30-60                                               2-amino-6-methyl-4-allyl-                                                                          250  30-60                                               __________________________________________________________________________

We claim:
 1. A method of avoiding the toxifying effect of a salt of aherbicidal bipyridylium quaternary cation which has been ingested by ahuman which comprises inducing emesis in said human with consequentremoval of the herbicidal salt from said human before lethal amounts ofthe herbicide can be assimilated by the body, said emesis being inducedby administering to said human an emetically effective amount of anemetically active s-triazolo (1,5-a) pyrimidine derivative of theformula: ##STR5## wherein R¹ is hydrogen, a C₁₋₄ alkyl radical, or aCOOEt radical; R² is a C₁₋₄ alkyl radical or an allyl radical, and R³ isa C₁₋₄ alkyl radical; or an addition salt thereof.